This invention relates to radiation dispersing cavities. More particularly, this invention relates to radiation dispersing cavities which rely upon a large number of interlocking deformations to the surface of the cavity to achieve a very close approximation to uniform Lambertian mixing of the input radiation.
Basically, this invention has two major embodiments, one as an optical integrating cavity and one as a black body emitter. The optical integrating cavity will be discussed first. An integrating cavity can be defined as a device which mixes radiation, whether polarized or Plankian or whatever, entering the cavity from different directions and emits uniformly mixed Lambertian distributed radiation. In most of the prior art devices, the emission of the uniformly mixed radiation is along a direction orthogonal to the source or sources of radiation at the input or inputs. The homogenized radiation is then dependent upon the sum of the spectral inputs and independent of any geometrical property of the input optics.
Most integrating cavities are spherical in shape. The integrating spheres in the prior art which are used in the visible portion of the spectrum are normally made by "smoking" the inside of a spherical cavity with magnesium oxide. The magnesium oxide is transparent to visible radiation, and, in its non-absorbing spectral regime, light is partly reflected from random facets at the outer surface of the magnesium oxide coating, partly transmitted and suffers reflection and refraction at each succeeding interface which it meets. Due to the random orientation of the porous magnesium oxide smoke and its low absorption, it randomizes the directed input radiation into a random Lambertian radiation distribution. U.S. Pat. No. 4,309,746 to Rushworth illustrates the employment of the magnesium oxide internal coating for the integrating cavity in its recitation in column 5. Another common coating employed in the prior art integrating cavities is barium sulphate. Its use is demonstrated in U.S. Pat. No. 4,232,971 to Suga in its teaching at column 4. It is important to note that these prior art devices rely upon the properties of the coating material itself to randomize the reflected radiation within the integrating cavity. This should be contrasted with the fundamentally different mechanism employed in the present invention in which the conformation of the cavity surface with its interlocking deformations produces the randomizing effect through the interaction of the light in the cavity with the individual reflecting elements. Unfortunately, since these prior art devices rely upon the optical properties of the coating materials emplaced upon the interior cavity surface, the effective bandwidth of the device is limited by the properties of the internal coating. Consequently, the integrating cavity technology of the prior art has not been able to be extended satisfactorily out of the visible portion of the optical spectrum, specifically not into the infrared bandwidths with satisfactory results. One U.S. Patent in the prior art, U.S. Pat. No. 3,319,071, to Werth et al., bears further comment. This reference describes the construction of a chamber used for measuring infrared absorption characteristics of gases in which the chamber bears a superficial resemblance to one embodiment of the integrating cavity of the present invention. However, the dimples which are formed in the surface of the prior art chamber are specifically designed such that the reflections therefrom will produce specular, rather than diffuse, reflections within the sphere, as is taught at the bottom of column 2 of this reference.